This application relates to antisense treatments for cancer making use of an antisense oligonucleotide that binds to testosterone-repressed prostate message-2 (TRPM-2).
Prostate cancer is the most common cancer that affects men, and the second leading cause of cancer deaths in men in the Western world. Because prostate cancer is an androgen-sensitive tumor, androgen withdrawal, for example via castration, is utilized in some therapeutic regimens for patients with advanced prostate cancer. Androgen withdrawal leads to extensive apoptosis in the prostate tumor, and hence to a regression of the disease. However, castration-induced apoptosis is not complete, and a progression of surviving tumor cells to androgen-independence ultimately occurs. This progression is the main obstacle to improving survival and quality of life, and efforts have therefore been made to target androgen-independent cells. These efforts have focused on non-hormonal therapies targeted against androgen-independent tumor cells (Yagoda et al., Cancer 71 (Supp. 3): 1098-1109 (1993); Oh et al., J. Urol. 60: 1220-1229 (1998)), however, so far no non-hormonal agent has improved survival.
TRPM-2 is a ubiquitous protein, with a diverse range of proposed activities. In prostate epithelial cell, expression of TRPM-2 increases immediately following castration, reaching peak levels in rat prostate cells at 3 to 4 days post castration, coincident with the onset of massive cell death. These results have led some researchers to the conclusion that TRPM-2 is a marker for cell death, and a promoter of apoptosis. On the other hand, the observation that Sertoli cells and some epithelial cells express high levels of TRPM-2 without increased levels of cell death, raises questions as to whether this conclusion is correct.
Sensibar et al., Cancer Research 55: 2431-2437(1995) reported on in vitro experiments performed to more clearly elucidate the role of TRPM-2 in prostatic cell death. They utilized LNCaP cells transfected with a gene encoding TRPM-2 and observed whether expression of this protein altered the effects of tumor necrosis factor α (TNFα), to which LNCaP cells are very sensitive, with cell death normally occurring within about 12 hours. Treatment of the transfected LNCaP cells with TNFα was shown to result in a transient increase in TRPM-2 levels for a period of a few hours, but these levels had dissipated by the time DNA fragmentation preceeding cell death was observed. Using an antisense molecule corresponding to the bases 1-21 of the TRPM-2 sequence, but not other TRPM-2 antisense oligonucleotides, resulted in a substantial reduction in expression of TRPM-2, and an increase in apoptotic cell death in LNCaP cells exposed to TNFα. This led Sensibar et al. to the hypothesis that overexpression of TRPM-2 could protect cells from the cytotoxic effect of TNF α, and that TRPM-2 depletion is responsible for the onset of cell death, although the mechanism of action remains unclear.
While Sensibar, et al. provides information about the possible role of TRPM-2, it nevertheless discloses results from only a model system in which expression of TRPM-2 is based on a transfected gene. Furthermore, expression levels of TRPM-2 is very low or absent in LNCaP cells grown in other labs. The situation which results in vivo when prostate tumor cells are subjected to androgen withdrawal is far more complex, with numerous proteins changing expression levels as a result. Thus, it is not possible from the Sensibar, et al. data to predict whether TRPM-2 would perform the same function when present in combination with other proteins, or whether changes in levels of TRPM-2 following androgen withdrawal in vivo could provide any therapeutic benefits. Indeed, the fact that TRPM-2 is expressed in substantial quantities in prostatic tumor cells at various stages following androgen withdrawal, including stages where significant apoptotic cell death is occurring suggests that role of TRPM-2 in vivo may be more complicated.
While the art provides data concerning certain aspects of apoptotic cell death in prostatic tumor cells, it offers neither a teaching nor a suggestion of a methodology to provide a delay in the onset of androgen-independence.